The present invention relates to an organic thin-film transistor including an active layer made of organic semiconductor and to a manufacturing method for the organic thin-film transistor. In particular, the invention relates to an organic thin-film transistor capable of being formed on a flexible base board made of a polymer material and a manufacturing method for the same.
With the spread of information terminals, there are increasing demands for a flat panel display that serves as a display for a computer. Further, with development of the information technology, there has been increased a chance for information offered in a form of a sheet of paper medium in the past to be offered in an electronic form. An electronic paper or a digital paper is demanded increasingly as a display medium for a mobile that is thin, lightweight and handy.
In the case of a display device of a flat sheet type, a display medium is generally formed by using an element that employs a liquid crystal, organic EL or electrophoretic method. In the display medium of this kind, a technology for using an active driving element (TFT element), serving as an image displaying element, is the main current for ensuring uniformity of screen brightness and a screen rewriting speed. For example, in the case of an ordinary computer display, a TFT element is formed on a glass base board, and a liquid crystal or organic EL is sealed.
In this case, a semiconductor such as a-Si (amorphous silicone) or p-Si (poly-silicone) can mainly be used for the TFT element, and these Si semiconductors (including also a metal film if necessary) are multi-layered, and source, drain and gate electrodes are formed on the base board in succession to manufacture the TFT element. The manufacture of the TFT element of this kind usually requires a process of sputtering and other manufacture process of a vacuum system.
On the other hand, recently, organic materials are studied to be used as an active semi-conductive layer in a thin-film transistor (TFT). Since the organic materials can be easily processed, and they have high affinity with a plastic base board on which TFT is formed generally, they are expected to be used as an active semi-conductive layer in a thin-film transistor. Therefore, they are studied as a low cost device having a large area, especially as an active driving element for a display, and there have been disclosed technologies in, for example, TOKKAIHEI No. 10-190001 and TOKKAI No. 2000-307172. In order for the organic semiconductor to be used as an active semiconductive layer in a thin-film TFT, conditions such as an ON/OFF ratio, leakage current, driving voltage of a gate of a device and insulation durability of the gate insulation layer, obtained as final result, need to be satisfied sufficiently.
However, in the manufacture of the TFT element of this kind, a manufacturing process of a vacuum system including a vacuum chamber needs to be repeated time after time to form various layers, resulting in a large amount of money in facility cost and running cost. For example, in the case of the TFT element shown in FIG. 9, steps of vacuum deposition, doping, photolithography and development need to be repeated time after time for forming various layers, and an element is formed on the base board through several tens of steps. Even for the semiconductor portions representing a vital point of switching operations, semiconductor layers in plural types such as a p-type and an n-type are laminated.
In the conventional manufacturing method employing a Si-semiconductor, drastic design changes in manufacturing apparatus such as vacuum chambers are required for the needs of large-sized display screens, and changes in apparatus are not easy.
Even in the case of a gate-insulating film of a transistor, it has been formed generally with a film of silicone oxide obtained through thermal oxidation of a silicone base board, or with a thin film of oxide obtained through a dry process such as a sputtering method, thus, formation of an insulating film had to rely on the conventional method even when using organic materials as an active semiconductor layer in TFT.
However, in order for the organic semiconductor to be used as an active semi-conductive layer in a thin-film TFT, conditions such as an ON/OFF ratio, leakage current and driving voltage of a gate of a device obtained finally need to be satisfied sufficiently. A practical method for realizing the aforementioned characteristics has not been found sufficiently.
To overcome the abovementioned drawbacks in conventional organic semiconductor devices, it is an object of the present invention to improve characteristics of organic semiconductor devices and thereby to realize reduction of manufacturing cost and simplification of manufacturing process.
Accordingly, to overcome the cited shortcomings, the abovementioned object of the present invention can be attained by organic semiconductor devices and methods described as follow.
(1) An organic semiconductor device, comprising: a drain electrode; a source electrode; a gate electrode; a channel that is made of an organic semiconductor material and is disposed between the drain electrode and the source electrode; and an insulation film that is disposed between the gate electrode and the channel; wherein the insulation film is formed under an atmospheric pressure environment by employing a plasma processing.
(2) The organic semiconductor device of item 1, wherein the insulation film comprises either oxide compounds or nitride compounds.
(3) The organic semiconductor device of item 2, wherein the insulation film comprises anyone of silicon oxide, aluminum oxide, tantalum oxide and titanium oxide.
(4) The organic semiconductor device of item 2, wherein the insulation film comprises silicon nitride.
(5) The organic semiconductor device of item 1, wherein the organic semiconductor material is xcfx80-conjugated polymers.
(6) The organic semiconductor device of item 1, wherein the organic semiconductor device is fabricated on a supporting substrate; and wherein the supporting substrate is a sheet made of a resin material.
(7) The organic semiconductor device of item 6, wherein the sheet is a plastic film.
(8) The organic semiconductor device of item 1, wherein the organic semiconductor device is fabricated on a supporting substrate; and wherein the supporting substrate is made of polymers.
(9) The organic semiconductor device of item 1, wherein the organic semiconductor device is fabricated on a supporting substrate; and wherein sections of the organic semiconductor device are formed in an order of the channel, the insulation film and the gate electrode.
(10) The organic semiconductor device of item 1, wherein the organic semiconductor device is a transistor.
(11) A method for manufacturing an organic semiconductor device, which includes a drain electrode, a source electrode and a gate electrode, comprising the steps of: forming a channel between the drain electrode and the source electrode with an organic semiconductor material; and forming an insulation film, disposed between a gate and the channel, under an atmospheric pressure environment by employing a plasma processing.
(12) The method of item 11, wherein a reactive gas is exited into plasma by a discharging operation under a pressure equivalent or nearly equivalent to an atmospheric pressure to form the insulation film.
(13) The method of item 11, wherein the organic semiconductor device is fabricated on a supporting substrate; and wherein, after the source electrode and the drain electrode are formed on the supporting substrate, a field-effect active layer, made of the organic semiconductor material, is fabricated between them as the channel, and then, the insulation film and the gate electrode are successively formed on the field-effect active layer.
(14) The method of item 11, wherein the organic semiconductor device is fabricated on a supporting substrate; and wherein, after the gate electrode is formed on the supporting substrate, the insulation film is formed so as to cover the gate electrode, and then, the source electrode, the drain electrode and a field-effect active layer, serving as the channel and made of the organic semiconductor material, are successively formed on the insulation film.
(15) The method of item 11, wherein the insulation film comprises either oxide compounds or nitride compounds.
(16) The method of item 15, wherein the insulation film comprises anyone of silicon oxide, aluminum oxide, tantalum oxide and titanium oxide.
(17) The method of item 15, wherein the insulation film comprises silicon nitride.
(18) The method of item 11, wherein the organic semiconductor material is xcfx80-conjugated polymers.
(19) The method of item 11, wherein the organic semiconductor device is fabricated on a supporting substrate; and wherein the supporting substrate is a sheet made of a resin material.
(20) The method of item 19, wherein the sheet is a plastic film.
(21) The method of item 11, wherein the organic semiconductor device is fabricated on a supporting substrate; and wherein the supporting substrate is made of polymers.
(22) The method of item 11, wherein the organic semiconductor device is fabricated on a supporting substrate; and further comprising the steps of: forming the source electrode and the drain electrode on the supporting substrate forming the gate electrode on the insulation film.
(23) The method of item 11, wherein the organic semiconductor device is a transistor.
(24) A display panel for displaying an image, comprising: a supporting substrate; and a plurality of organic semiconductor devices formed on the supporting substrate; wherein each of the plurality of organic semiconductor devices comprises: a drain electrode; a source electrode; a gate electrode; a channel that is made of an organic semiconductor material and is disposed between the drain electrode and the source electrode; and an insulation film that is disposed between the gate electrode and the channel; wherein the insulation film is formed under an atmospheric pressure environment by employing a plasma processing.